1. Field of the Invention
This invention relates generally to gypsum board and its manufacture, and more specifically, relates to gypsum board having at least one face or surface capable of receiving and adhering to polymeric coatings and a manufacturing process permitting the targeted delivery of the polymeric coatings to specified locations.
2. Background Art
Gypsum board, and its production, has received attention in the building industry, and especially for providing an easily worked building material the consistency of which is available for general construction use. Desirable characteristics for gypsum board also include a smooth working surface, consistent thickness throughout, and the ability to provide finishing enhancements, such as paint or other protective coverings, thereon.
Recent developments in the manufacture of gypsum board have also added to the durability and versatility of the uses to which gypsum boards may be put. For a fuller discussion of the developments in the building board field is known as glass reinforced gypsum (GRG) board, reference is made to the aforementioned U.S. Pat. No. 6,524,679, commonly owned with the present invention, and incorporated by reference has if fully disclosed herein.
Manufacturing facilities for the production of gypsum board, whether or not glass mats are utilized for the structural facings, are capital intensive in the costs of space, equipment and in the down time during which a gypsum board production line is reconfigured. For production of a variety of gypsum board products, for example, standard paper faced gypsum board, glass mat backed board, etc., down time of the production line represents a significant cost in the delay of production of gypsum board and in time wasted by production workers who remain idle.
It has been further found that further finishing, e.g., painting of a smooth gypsum board surface, is made easier because the need for additional prefinishing steps, such as priming, etc., may be minimized.
In addition, gypsum products, e.g., wallboard, tile, block, casts and the like, have relatively little resistance to water when not modified by some chemical or physical modification to address the problem of water absorption by the gypsum board. When gypsum wallboard, for example, is immersed in water, the board may quickly absorb a considerable amount of water, lose a great deal of its integrity and structural strength, and distort or swell in different places. Many attempts have been made in the past to improve the water resistance of gypsum products by adding waterproofing materials within the gypsum slurry. The most common waterproofing material being used is a hydrophobic emulsion, usually an emulsion comprising wax, paraffin, asphalt or a silicone compound, e.g., silanes and siloxanes.
As can be expected, modification of gypsum slurry to render it water resistant adds to the cost of gypsum production, both in terms of the cost of the added substance, and in terms of the additional equipment necessary to mix and deliver the water resisting compounds to the gypsum slurry before application. Thus, it has been found desirable to provide a gypsum board and manufacturing process thereof which can be manufactured at relatively high speed, has high structural integrity and strength by virtue of using a mat of relatively low diameter fibers, and may include in a face coating a polymeric additive material providing a surface ideal for further finishing of the gypsum board, in addition to a means for delivering the water resistant material targeted to the location on the gypsum board where it would be most useful, that is on the surface of the finished gypsum board product. While the water resistant capability is desirable for all of the gypsum layers in a gypsum board, it is now possible to target specified layers of a multiplayer gypsum board that is made in accordance with the aforementioned U.S. Pat. No. 6,524,679, and other multilayer boards.
As a result of further development obtained through practice and further consideration of the concepts disclosed and claimed the aforementioned U.S. Pat. No. 6,524,679, it has been found additionally desirable to provide a means for delivering specific desired additives to a specified multilayer density layer of a gypsum board panel, in order to obtain specified desirable properties. For example, it has been found desirable to increase the water resistance of the outer face surface of a glass mat gypsum panel made in accordance with the teachings in the aforementioned U.S. Pat. No. 6,524,679. Moreover, in accordance with the teachings of that patent, the additives should only be targeted to that layer, for example, the dense slurry layer, in which it is desirable to provide the desired characteristic, so as to avoid unnecessary cost and weight to the final board panel by adding costly and sometimes denser additives to layers of the gypsum board that will not provide as much benefit as those to which the additives are targeted.